Setting Expansion Characteristics of Three Phosphate-Bonded Investment Materials Used with High Fusing High-Noble Alloys, Cobalt-Chrome Alloys and Heat-Pressed Lithium Disilicate Ceramics

Abstract

The purpose of this study was to investigate the setting expansion characteristics of three commercially available phosphate bonded investment materials for casting high fusing alloys and heat pressed lithium disilicate. The experimental groups in this study were P90 (Powercast 90% Special Liquid for Cobalt-Chrome alloys), P60 (Powercast 60% Special Liquid for High Noble Gold alloys), FF75 (FastFire 15 75% Special Liquid for Cobalt-Chrome alloys), FF50 (FastFire 15 50% Special Liquid for High Noble Gold alloys), and PVS (PressVest Speed 60% Special Liquid for Lithium Disilicate Veneers, Partial Crowns and Single Crowns). Twenty specimens per group were poured in a trough that conformed to ADA Specification No. 2 for the measurement of the linear setting expansion of gypsum bonded investments. Measurements of the setting expansion were taken at 2, 4, 6, 8, 12, and 24 hours after mixing. A one sample T-Test revealed that the setting expansion measured for all of the groups was statistically significant and that all of the groups exhibited statistically significant differences in setting expansion at the manufacturer’s recommended burn-out time from the setting expansion reported by the manufacturer (P≤0.01). P90, P60, FF50 and PVS showed less expansion than is required in order to fully compensate for solidification shrinkage during the casting procedures. FF75 was the only group that managed to fully compensate for the solidification shrinkage of the alloy it is intended for (P≤0.01). The delayed burn-out times evaluated in this study resulted in significantly different setting expansion for PVS. A statistically significant difference was detected after 4 hours. The dimension of the PVS specimens did not change significantly after 4 hours. No such difference in setting expansion at delayed burn-out times could be detected for P90, P60, FF75 & FF50 (P≤0.01). Within the limitations of this study, the setting expansion of the phosphate bonded investment materials tested could not fully compensate for the solidification shrinkage of the alloys except for FF75. Delayed burn-out times resulted in significantly different setting expansion for PVS. Significant differences at delayed burn-out times could not be detected for the rest of the groups